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E. Meroni

Publications and source records attributed to E. Meroni.

At least 37 records · Page 2Linked to original sources
arXiv2020

Constraints on Flavor-Diagonal Non-Standard Neutrino Interactions from Borexino Phase-II

The Borexino detector measures solar neutrino fluxes via neutrino-electron elastic scattering. Observed spectra are determined by the solar-$ν_{e}$ survival probability $P_{ee}(E)$, and the chiral couplings of the neutrino and electron. Some theories of physics beyond the Standard Model postulate the existence of Non-Standard Interactions (NSI's) which modify the chiral couplings and $P_{ee}(E)$. In this paper, we search for such NSI's, in particular, flavor-diagonal neutral current interactions that modify the $ν_e e$ and $ν_τe$ couplings using Borexino Phase II data. Standard Solar Model predictions of the solar neutrino fluxes for both high- and low-metallicity assumptions are considered. No indication of new physics is found at the level of sensitivity of the detector and constraints on the parameters of the NSI's are placed. In addition, with the same dataset the value of $\sin^2θ_W$ is obtained with a precision comparable to that achieved in reactor antineutrino experiments.

hep-ph↗
arXiv2019

Simultaneous Precision Spectroscopy of $pp$, $^7$Be, and $pep$ Solar Neutrinos with Borexino Phase-II

We present the first simultaneous measurement of the interaction rates of $pp$, $^7$Be, and $pep$ solar neutrinos performed with a global fit to the Borexino data in an extended energy range (0.19-2.93)$\,$MeV. This result was obtained by analyzing 1291.51$\,$days of Borexino Phase-II data, collected between December 2011 and May 2016 after an extensive scintillator purification campaign. We find: rate($pp$)$\,$=$\,$$134$$\,$$\pm$$\,$$10$$\,$($stat$)$\,$$^{\rm +6}_{\rm -10}$$\,$($sys$)$\,$cpd/100$\,$t, rate($^7$Be)$\,$=$\,$$48.3$$\,$$\pm$$\,$$1.1$$\,$($stat$)$\,$$^{\rm +0.4}_{\rm -0.7}$$\,$($sys$)$\,$cpd/100$\,$t, and rate($pep$)$\,$=$\,$$2.43$$\pm$$\,$$0.36$$\,$($stat$)$^{+0.15}_{-0.22}$$\,$($sys$)$\,$cpd/100$\,$t. These numbers are in agreement with and improve the precision of our previous measurements. In particular, the interaction rate of $^7$Be $ν$'s is measured with an unprecedented precision of 2.7%, showing that discriminating between the high and low metallicity solar models is now largely dominated by theoretical uncertainties. The absence of $pep$ neutrinos is rejected for the first time at more than 5$\,$$σ$. An upper limit of $8.1$$\,$cpd/100$\,$t (95%$\,$C.L.) on the CNO neutrino rate is obtained by setting an additional constraint on the ratio between the $pp$ and $pep$ neutrino rates in the fit. This limit has the same significance as that obtained by the Borexino Phase-I (currently providing the tightest bound on this component), but is obtained by applying a less stringent constraint on the $pep$ $ν$ flux.

hep-ex↗
arXiv2019

$^{222}$Rn contamination mechanisms on acrylic surfaces

In this work, the $^{222}$Rn contamination mechanisms on acrylic surfaces have been investigated. $^{222}$Rn can represent a significant background source for low-background experiments, and acrylic is a suitable material for detector design thanks to its purity and transparency. Four acrylic samples have been exposed to a $^{222}$Rn rich environment for different time periods, being contaminated by $^{222}$Rn and its progenies. Subsequently, the time evolution of radiocontaminants activity on the samples has been evaluated with $α$ and $γ$ measurements, highlighting the role of different decay modes in the contamination process. A detailed analysis of the alpha spectra allowed to quantify the implantation depth of the contaminants. Moreover, a study of both $α$ and $γ$ measurements pointed out the $^{222}$Rn diffusion inside the samples.

physics.ins-det↗
arXiv2019

Search for low-energy neutrinos from astrophysical sources with Borexino

We report on searches for neutrinos and antineutrinos from astrophysical sources performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso in Italy. Electron antineutrinos ($\barν_e$) are detected in an organic liquid scintillator through the inverse $β$-decay reaction. In the present work we set model-independent upper limits in the energy range 1.8-16.8 MeV on neutrino fluxes from unknown sources that improve our previous results, on average, by a factor 2.5. Using the same data set, we first obtain experimental constraints on the diffuse supernova $\barν_e$ fluxes in the previously unexplored region below 8 MeV. A search for $\barν_e$ in the solar neutrino flux is also presented: the presence of $\barν_e$ would be a manifestation of a non-zero anomalous magnetic moment of the neutrino, making possible its conversion to antineutrinos in the strong magnetic field of the Sun. We obtain a limit for a solar $\barν_e$ flux of 384 cm$^{-2}$s$^{-1}$ (90% C.L.), assuming an undistorted solar $^{8}$B neutrinos energy spectrum, that corresponds to a transition probability $p_{ ν_e \rightarrow \barν_{e}}<$ 7.2$\times$10$^{-5}$ (90% C.L.) for E$_{\bar ν_e}$ $>$ 1.8 MeV. At lower energies, by investigating the spectral shape of elastic scattering events, we obtain a new limit on solar $^{7}$Be-$ν_e$ conversion into $\barν_e$ of $p_{ ν_e \rightarrow \bar ν_{e}}<$ 0.14 (90% C.L.) at 0.862 keV. Last, we investigate solar flares as possible neutrino sources and obtain the strongest up-to-date limits on the fluence of neutrinos of all flavor neutrino below 3-7 ,MeV. Assuming the neutrino flux to be proportional to the flare's intensity, we exclude an intense solar flare as the cause of the observed excess of events in run 117 of the Cl-Ar Homestake experiment.

hep-ex↗
arXiv2019

Distillation and stripping pilot plants for the JUNO neutrino detector: design, operations and reliability

This paper describes the design, construction principles and operations of the distillation and stripping pilot plants tested at the Daya Bay Neutrino Laboratory, with the perspective to adapt this processes, system cleanliness and leak-tightness to the final full scale plants that will be used for the purification of the liquid scintillator used in the JUNO neutrino detector. The main goal of these plants is to remove radio impurities from the liquid scintillator while increasing its optical attenuation length. Purification of liquid scintillator will be performed with a system combining alumina oxide, distillation, water extraction and steam (or N2 gas) stripping. Such a combined system will aim at obtaining a total attenuation length greater than 20 m at 430 nm, and a bulk radiopurity for 238U and 232Th in the 10-15 to 10-17 g/g range. The pilot plants commissioning and operation have also provided valuable information on the degree of reliability of their main components, which will be particularly useful for the design of the final full scale purification equipment for the JUNO liquid scintillator. This paper describe two of the five pilot plants since the Alumina Column, Fluor mixing and the Water Extraction plants are in charge of the Chinese part of the collaboration.

physics.ins-det↗
arXiv2019

Modulations of the Cosmic Muon Signal in Ten Years of Borexino Data

We have measured the flux of cosmic muons in the Laboratori Nazionali del Gran Sasso at 3800\,m\,w.e. to be $(3.432 \pm 0.003)\cdot 10^{-4}\,\mathrm{{m^{-2}s^{-1}}}$ based on ten years of Borexino data acquired between May 2007 and May 2017. A seasonal modulation with a period of $(366.3 \pm 0.6)\,\mathrm{d}$ and a relative amplitude of $(1.36 \pm0.04)\%$ is observed. The phase is measured to be $(181.7 \pm 0.4)\,\mathrm{d}$, corresponding to a maximum at the 1$^\mathrm{st}$ of July. Using data inferred from global atmospheric models, we show the muon flux to be positively correlated with the atmospheric temperature and measure the effective temperature coefficient $α_\mathrm{T} = 0.90 \pm 0.02$. The origin of cosmic muons from pion and kaon decays in the atmosphere allows to interpret the effective temperature coefficient as an indirect measurement of the atmospheric kaon-to-pion production ratio $r_{\mathrm{K}/π} = 0.11^{+0.11}_{-0.07}$ for primary energies above $18\,\mathrm{TeV}$. We find evidence for a long-term modulation of the muon flux with a period of $\sim 3000\,\mathrm{d}$ and a maximum in June 2012 that is not present in the atmospheric temperature data. A possible correlation between this modulation and the solar activity is investigated. The cosmogenic neutron production rate is found to show a seasonal modulation in phase with the cosmic muon flux but with an increased amplitude of $(2.6 \pm 0.4)\%$.

hep-ex↗
arXiv2019

GIGJ: a crustal gravity model of the Guangdong Province for predicting the geoneutrino signal at the JUNO experiment

Gravimetric methods are expected to play a decisive role in geophysical modeling of the regional crustal structure applied to geoneutrino studies. GIGJ (GOCE Inversion for Geoneutrinos at JUNO) is a 3D numerical model constituted by ~46 x 10$^{3}$ voxels of 50 x 50 x 0.1 km, built by inverting gravimetric data over the 6° x 4° area centered at the Jiangmen Underground Neutrino Observatory (JUNO) experiment, currently under construction in the Guangdong Province (China). The a-priori modeling is based on the adoption of deep seismic sounding profiles, receiver functions, teleseismic P-wave velocity models and Moho depth maps, according to their own accuracy and spatial resolution. The inversion method allowed for integrating GOCE data with the a-priori information and regularization conditions through a Bayesian approach and a stochastic optimization. GIGJ fits the homogeneously distributed GOCE gravity data, characterized by high accuracy, with a ~1 mGal standard deviation of the residuals, compatible with the observation accuracy. Conversely to existing global models, GIGJ provides a site-specific subdivision of the crustal layers masses which uncertainties include estimation errors, associated to the gravimetric solution, and systematic uncertainties, related to the adoption of a fixed sedimentary layer. A consequence of this local rearrangement of the crustal layer thicknesses is a ~21% reduction and a ~24% increase of the middle and lower crust expected geoneutrino signal, respectively. Finally, the geophysical uncertainties of geoneutrino signals at JUNO produced by unitary uranium and thorium abundances distributed in the upper, middle and lower crust are reduced by 77%, 55% and 78%, respectively. The numerical model is available at http://www.fe.infn.it/u/radioactivity/GIGJ

physics.geo-ph↗
arXiv2018

Nanoseconds Timing System Based on IEEE 1588 FPGA Implementation

Clock synchronization procedures are mandatory in most physical experiments where event fragments are readout by spatially dislocated sensors and must be glued together to reconstruct key parameters (e.g. energy, interaction vertex etc.) of the process under investigation. These distributed data readout topologies rely on an accurate time information available at the frontend, where raw data are acquired and tagged with a precise timestamp prior to data buffering and central data collecting. This makes the network complexity and latency, between frontend and backend electronics, negligible within upper bounds imposed by the frontend data buffer capability. The proposed research work describes an FPGA implementation of IEEE 1588 Precision Time Protocol (PTP) that exploits the CERN Timing, Trigger and Control (TTC) system as a multicast messaging physical and data link layer. The hardware implementation extends the clock synchronization to the nanoseconds range, overcoming the typical accuracy limitations inferred by computers Ethernet based Local Area Network (LAN). Establishing a reliable communication between master and timing receiver nodes is essential in a message-based synchronization system. In the backend electronics, the serial data streams synchronization with the global clock domain is guaranteed by an hardware-based finite state machine that scans the bit period using a variable delay chain and finds the optimal sampling point. The validity of the proposed timing system has been proved in point-to-point data links as well as in star topology configurations over standard CAT-5e cables. The results achieved together with weaknesses and possible improvements are hereby detailed.

cs.NI↗
arXiv2018

Speeding up complex multivariate data analysis in Borexino with parallel computing based on Graphics Processing Unit

A spectral fitter based on the graphics processor unit (GPU) has been developed for Borexino solar neutrino analysis. It is able to shorten the fitting time to a superior level compared to the CPU fitting procedure. In Borexino solar neutrino spectral analysis, fitting usually requires around one hour to converge since it includes time-consuming convolutions in order to account for the detector response and pile-up effects. Moreover, the convergence time increases to more than two days when including extra computations for the discrimination of $^{11}$C and external $γ$s. In sharp contrast, with the GPU-based fitter it takes less than 10 seconds and less than four minutes, respectively. This fitter is developed utilizing the GooFit project with customized likelihoods, pdfs and infrastructures supporting certain analysis methods. In this proceeding the design of the package, developed features and the comparison with the original CPU fitter are presented.

physics.data-an↗
arXiv2018

Charge reconstruction in large-area photomultipliers

Large-area PhotoMultiplier Tubes (PMT) allow to efficiently instrument Liquid Scintillator (LS) neutrino detectors, where large target masses are pivotal to compensate for neutrinos' extremely elusive nature. Depending on the detector light yield, several scintillation photons stemming from the same neutrino interaction are likely to hit a single PMT in a few tens/hundreds of nanoseconds, resulting in several photoelectrons (PEs) to pile-up at the PMT anode. In such scenario, the signal generated by each PE is entangled to the others, and an accurate PMT charge reconstruction becomes challenging. This manuscript describes an experimental method able to address the PMT charge reconstruction in the case of large PE pile-up, providing an unbiased charge estimator at the permille level up to 15 detected PEs. The method is based on a signal filtering technique (Wiener filter) which suppresses the noise due to both PMT and readout electronics, and on a Fourier-based deconvolution able to minimize the influence of signal distortions ---such as an overshoot. The analysis of simulated PMT waveforms shows that the slope of a linear regression modeling the relation between reconstructed and true charge values improves from $0.769 \pm 0.001$ (without deconvolution) to $0.989 \pm 0.001$ (with deconvolution), where unitary slope implies perfect reconstruction. A C++ implementation of the charge reconstruction algorithm is available online at http://www.fe.infn.it/CRA .

physics.ins-det↗
arXiv2017

Limiting neutrino magnetic moments with Borexino Phase-II solar neutrino data

A search for the solar neutrino effective magnetic moment has been performed using data from 1291.5 days exposure during the second phase of the Borexino experiment. No significant deviations from the expected shape of the electron recoil spectrum from solar neutrinos have been found, and a new upper limit on the effective neutrino magnetic moment of $μ_ν^{eff}$ $<$ 2.8$\cdot$10$^{-11}$ $μ_{B}$ at 90\% c.l. has been set using constraints on the sum of the solar neutrino fluxes implied by the radiochemical gallium experiments.Using the limit for the effective neutrino moment, new limits for the magnetic moments of the neutrino flavor states, and for the elements of the neutrino magnetic moments matrix for Dirac and Majorana neutrinos, are derived.

hep-ex↗
arXiv2017

A search for low-energy neutrinos correlated with gravitational wave events GW150914, GW151226 and GW170104 with the Borexino detector

We present the results of a low-energy neutrino search using the Borexino detector in coincidence with the gravitational wave (GW) events GW150914, GW151226 and GW170104. We searched for correlated neutrino events with energies greater than 250 keV within a time window of $\pm500$ s centered around the GW detection time. A total of five candidates were found for all three GW150914, GW151226 and GW170104. This is consistent with the number of expected solar neutrino and background events. As a result, we have obtained the best current upper limits on the GW event neutrino fluence of all flavors ($ν_e, ν_μ, ν_τ$) in the energy range $(0.5 - 5.0)$ MeV.

astro-ph.HE↗
arXiv2017

Seasonal Modulation of the $^7$Be Solar Neutrino Rate in Borexino

We detected the seasonal modulation of the $^7$Be neutrino interaction rate with the Borexino detector at the Laboratori Nazionali del Gran Sasso in Italy. The period, amplitude, and phase of the observed time evolution of the signal are consistent with its solar origin, and the absence of an annual modulation is rejected at 99.99\% C.L. The data are analyzed using three methods: the sinusoidal fit, the Lomb-Scargle and the Empirical Mode Decomposition techniques, which all yield results in excellent agreement.

hep-ex↗
arXiv2017

The Monte Carlo simulation of the Borexino detector

We describe the Monte Carlo (MC) simulation package of the Borexino detector and discuss the agreement of its output with data. The Borexino MC 'ab initio' simulates the energy loss of particles in all detector components and generates the resulting scintillation photons and their propagation within the liquid scintillator volume. The simulation accounts for absorption, reemission, and scattering of the optical photons and tracks them until they either are absorbed or reach the photocathode of one of the photomultiplier tubes. Photon detection is followed by a comprehensive simulation of the readout electronics response. The algorithm proceeds with a detailed simulation of the electronics chain. The MC is tuned using data collected with radioactive calibration sources deployed inside and around the scintillator volume. The simulation reproduces the energy response of the detector, its uniformity within the fiducial scintillator volume relevant to neutrino physics, and the time distribution of detected photons to better than 1% between 100 keV and several MeV. The techniques developed to simulate the Borexino detector and their level of refinement are of possible interest to the neutrino community, especially for current and future large-volume liquid scintillator experiments such as Kamland-Zen, SNO+, and Juno.

physics.ins-det↗
arXiv2016

A search for low-energy neutrino and antineutrino signals correlated with gamma-ray bursts with Borexino

A search for neutrino and antineutrino events correlated with 2,350 gamma-ray bursts (GRBs) is performed with Borexino data collected between December 2007 and November 2015. No statistically significant excess over background is observed. We look for electron antineutrinos ($\barν_e$) that inverse beta decay on protons with energies from 1.8\,MeV to 15\,MeV and set the best limit on the neutrino fluence from GRBs below 8\,MeV. The signals from neutrinos and antineutrinos from GRBs that scatter on electrons are also searched for, a detection channel made possible by the particularly radio-pure scintillator of Borexino. We obtain currently the best limits on the neutrino fluence of all flavors and species below 7\,MeV. Finally, time correlations between GRBs and bursts of events are investigated. Our analysis combines two semi-independent data acquisition systems for the first time: the primary Borexino readout optimized for solar neutrino physics up to a few MeV, and a fast waveform digitizer system tuned for events above 1\,MeV.

astro-ph.HE↗
arXiv2015

A test of electric charge conservation with Borexino

Borexino is a liquid scintillation detector located deep underground at the Laboratori Nazionali del Gran Sasso (LNGS, Italy). Thanks to the unmatched radio-purity of the scintillator, and to the well understood detector response at low energy, a new limit on the stability of the electron for decay into a neutrino and a single mono-energetic photon was obtained. This new bound, tau > 6.6 10**28 yr at 90 % C.L., is two orders of magnitude better than the previous limit.

hep-ex↗
arXiv2015

Low-energy (anti)neutrino physics with Borexino: Neutrinos from the primary proton-proton fusion process in the Sun

The Sun is fueled by a series of nuclear reactions that produce the energy that makes it shine. The primary reaction is the fusion of two protons into a deuteron, a positron and a neutrino. These neutrinos constitute the vast majority of neutrinos reaching Earth, providing us with key information about what goes on at the core of our star. Several experiments have now confirmed the observation of neutrino oscillations by detecting neutrinos from secondary nuclear processes in the Sun; this is the first direct spectral measurement of the neutrinos from the keystone proton-proton fusion. This observation is a crucial step towards the completion of the spectroscopy of pp-chain neutrinos, as well as further validation of the LMA-MSW model of neutrino oscillations.

hep-ex↗